Known subsonic cartridge ammunition typically includes a projectile and a high-pressure, low-pressure propulsion system for expelling the projectile from the cartridge case. The high-pressure, low-pressure propulsion system comprises a high pressure chamber in the base of the cartridge case which houses a propelling charge and a low pressure chamber surrounding the high pressure chamber. The high pressure chamber has one or more vent openings leading into the low pressure chamber, for expanding propellant gases.
Subsonic cartridge ammunition of the abovementioned type is known to suffer from a number of limitations, including that the propelling charge is often not combusted completely within the high pressure chamber resulting in uncombusted propellant being expelled from the high pressure chamber into the low pressure chamber. A portion of the uncombusted propellant is combusted in the low pressure chamber. However, this has little or no significant propulsion effect on the projectile. A further portion of the uncombusted propellant is wasted as it is discharged along the barrel of the firing weapon.
The Applicant has found that in addition to combustion of propellant in such dual chamber ammunition being inefficient, the amount of the propelling charge which is combusted in the high pressure is inconsistent in such dual chamber cartridge ammunition. Inconsistent combustion of propellant in such dual chamber cartridge ammunition results in inconsistent propellant gas pressures and as a consequence, inconsistent muzzle velocities of projectiles resulting in inaccurate firing. Furthermore, it is not possible to achieve a satisfactory level of control over pressures exerted on the barrels of weapons firing such ammunition, particularly if the cartridge ammunition has been modified so as to achieve an extended range capability.
Generally accepted design criteria used in the design of small to medium calibre subsonic ammunition, include the design of the projectile such that a portion of the projectile which is located within the cartridge case of the ammunition, occupies a minimal volume within the cartridge case so as to provide for maximum internal free volume for expanding propellant gases. It will be appreciated that a reduction in the internal free volume within the cartridge case will result in an increase in gas pressure within the free volume. A relatively large free volume within the cartridge thus acts as a pressure attenuator for propellant gas pressure peaks within the cartridge case. Exposure of weapon chambers to high pressure peaks is clearly unsatisfactory as such exposure may cause damage to the firing weapon and also result in possible injury or death to operators of a firing weapon.
As evidence of the abovementioned design criteria, weapon manufacturers are generally unwilling to endorse the use of enhanced ammunition configurations on their weapons where such enhancements may include, for example, heavier projectiles or extended firing ranges, as the potential for failure is too high due to resultant peak weapon chamber pressures in excess of standard pressures which the weapons were designed to endure in the field.
It is an object of the present invention to ameliorate the abovementioned limitations of known conventional cartridge ammunition.
It is a further object of the present invention to provide cartridge ammunition which meets the abovementioned design criteria and more specifically, which provides for attenuation of high pressure peaks in the weapon chambers of firing weapons.